Rates of heroin addiction are increasing worldwide with concomitant legal, health, and personal costs, including increased risk of HIV transmission. Heroin addiction is commonly associated with neurocognitive deficits in impulsivity, such as impaired decision-making, increased risk-taking, and delayed reward discounting. Such neurocognitive deficits may be related to engagement in risky sexual and injection behaviors, some of the primary vectors for HIV transmission. However, relative to other illicit drugs, considerably less research exists on the neurocognitive sequelae of chronic heroin use and how they relate to HIV risk behaviors. Further, most existing studies include polysubstance users, which makes it impossible to distinguish the neurocognitive effects of heroin from those of other drugs. We propose to develop a program of studies with the long-term goal of understanding how neurocognitive aspects of impulsivity relate to HIV risk behaviors in heroin users. This program will be developed in Bulgaria, a low-middle income country in Southeastern Europe and a key country on the `Balkan Drug Route', one of the main routes for international drug traffic from South-West Asia to Western Europe. Heroin is easily available in the country and heroin addiction has become one of the most significant public health problems. Patterns of heroin addiction in Bulgaria are unique in that polysubstance dependence is uncommon. Moreover, although currently the prevalence of HIV in Bulgaria is still low, the country is considered to be at the brink of an HIV epidemic, as it is located in a region experiencing the world's fastest-growing rates of HIV infection. Therefore, conducting the study in a developing country with very limited health-care resources could have critical public health implications by informing HIV prevention efforts prior to onset of a full-fledged HIV epidemic. Furthermore, conducting the study in Bulgaria provides a unique opportunity to study how neurocognitive function relates to HIV risk behaviors in populations of "pure" heroin users, thereby avoiding the confounding effects of polysubstance use. Our specific aims for this R21 pilot study are to expand our already established international research collaboration and develop a protocol for initial neurocognitive assessment of impulsivity and HIV risk behaviors in substance dependent individuals (SDIs) by adapting North American laboratory neurocognitive tasks of impulsivity and assessment questionnaires for culturally-appropriate use in Bulgaria. We will also explore the feasibility of collecting exploratory data about the associations between different neurocognitive indices of impulsivity and HIV risk behaviors among an existing cohort of 50 non-polysubstance using heroin dependent subjects. Study results will provide pilot data and be used to design a larger study of neurocognition and HIV risk behaviors in SDIs with the ultimate goal of helping prevention and intervention programs by developing measures that could be used as "neurocognitive markers" of HIV risk behaviors in SDIs. RELEVANCE The focus of the project on how neurocognitive indices of impulsivity relate to HIV risk behaviors in substance dependent individuals (SDIs) is expected to have important implications for prevention and intervention programs by developing measures that could be used as "neurocognitive markers" of HIV risk behaviors in SDIs. Further, the project may help reduce the costs of current prevention and intervention programs by identifying individuals most vulnerable to engaging in HIV risk behaviors who should be targeted first by prevention and intervention programs. [unreadable] [unreadable] [unreadable]